1. Field
The present disclosure pertains to the field of information processing, and more particularly, to the field of using performance counters in a virtualization environment.
2. Description of Related Art
Generally, the concept of virtualization in information processing systems allows multiple instances of one or more operating systems (each, an “OS”) to run on a single information processing system, even though each OS is designed to have complete, direct control over the system and its resources. Virtualization is typically implemented by using software (e.g., a virtual machine monitor, or a “VMM”) to present to each OS a “virtual machine” (“VM”) having virtual resources, including one or more virtual processors, that the OS may completely and directly control, while the VMM maintains a system environment for implementing virtualization policies such as sharing and/or allocating the physical resources among the VMs (the “virtualization environment”). Each OS, and any other software, that runs on a VM is referred to as a “guest” or as “guest software,” while a “host” or “host software” is software, such as a VMM, that runs outside of the virtualization environment.
A physical processor in an information processing system may support virtualization, for example, by supporting an instruction to enter a virtualization environment to run a guest on a virtual processor (i.e., a physical processor under constraints imposed by a VMM) in a VM. In the virtualization environment, certain events, operations, and situations, such as external interrupts or attempts to access privileged registers or resources, may be intercepted, i.e., cause the processor to exit the virtualization environment so that a VMM may operate, for example, to implement virtualization policies. A physical processor may also support other instructions for maintaining a virtualization environment, and may include memory or register bits that indicate or control virtualization capabilities of the physical processor.
A physical processor supporting a virtualization environment may include performance counters for logging performance monitoring information. Typically, each performance counter would be controlled by one or more control or configuration registers, or portions of a one or more control or configuration registers, associated with the counter. To virtualize these performance counters, each transition between a guest and a host or between two guests would typically require saving the state of all of the counters and their associated control registers and loading a new state for all of the counters and their associated control registers.